As well known to those skilled in the art, the so called needle-shaped toothbrush bristles having tapered ends have been widely used in recent years, because of easier removal of impurities between the teeth or the tooth and the gum of the user with excellent scaling function, compared to conventional toothbrush bristles.
Such needle-shaped bristles may be manufactured by mechanically grinding the ends of toothbrush bristles. But, this process is disadvantageous in light of high manufacturing cost. As well, the above toothbrush bristles have shortly tapered lengths and needle-shaped ends, and thus the bristles may injure the gum of the user. Hence, the toothbrush bristles obtained by the above-mentioned process are unsuitable for use in toothbrushes.
Alternatively, there are developed methods of tapering the ends of toothbrush bristles by suitably dissolving the ends of the toothbrush bristles in a chemicals, such as an acid or alkali, to have a sufficiently tapered length, and such a method is representatively exemplified by Korean Patent No. 130932 invented by the present inventors.
The method disclosed in Korean Patent No. 130932 comprises the steps of (i) cutting a toothbrush bristle made of PBT or PET to a desired length, (ii) vertically immersing an end of the cut toothbrush bristle to a depth of 8-9 mm in 60-98% sulfuric acid solution at 80-200° C. so as to taper it, followed by treating the other end of the toothbrush bristle in the same manner as in this step, (iii) cooling the tapered toothbrush bristle in cooling water, (iv) neutralizing the cooled toothbrush bristle with 30-70% caustic soda or potassium hydroxide solution, and (v) washing the neutralized toothbrush bristle with water and drying it.
Thusly obtained toothbrush bristles have needle-shaped sharp ends each having a tapered length of 4-8 mm and a tip with a diameter of 0.01-0.02 mm as shown in FIG. 1. Such toothbrush bristles are referred to as “highly tapered toothbrush bristles”.
Although the highly tapered toothbrush bristles have the sharp ends as in a needle, the bristles have a long tapered length and are soft, and do not injure the gum of the user. Further, when the above toothbrush bristles are used, scaling function between the teeth or in the periodontal pockets may be easily performed.
However, the highly tapered toothbrush bristles have the following drawbacks.
First, even under the fixed conditions of concentration, temperature and immersion time of the used chemicals, it is difficult to manufacture the toothbrush bristles having regularly tapered lengths and end points each with a uniform diameter, depending on the immersion position and the immersed bristle number.
Second, when the toothbrush bristles are excessively dissolved, the bristles have a shorter length than a desired length. In contrast, the toothbrush bristles may also be undesirably long, therefore resulting in increased defective rates.
Third, too-soft toothbrush bristles result in unsatisfactory feeling after using the toothbrush, according to the users.
Fourth, the toothbrush bristles have very short service life and are expensive.
Therefore, with the aim of solving the above problems, there are proposed conventional techniques, for example, Korean Utility Model No. 114700 and Korean Patent No. 261658 by the present inventors.
In Korean Utility Model No. 114700, an end of a toothbrush bristle is tapered up to ¼ of its length from a terminal point of the bristle (eg., 8 mm when a toothbrush bristle is 32 mm long), and the other end thereof is tapered up to ⅛ of its length from the other terminal point (4 mm when a toothbrush bristle is 32 mm long), thereby obtaining the toothbrush bristle having differently tapered ends (8mm, 4 mm), which is then disposed on a toothbrush. Therefore, this toothbrush has a certain extent of hardness, in addition to a scaling function and a plaque-removing function.
Additionally, in Korean Patent No. 261658, a toothbrush bristle made of PBT has both end points each with a diameter of 0.04-0.08 mm, provided that it is manufactured by the same method as in Korean Patent No. 130932. The above patent is advantageous in light of low manufacturing cost of the tapered toothbrush bristle, because of using a physical tapering method and a chemical tapering method together. Thusly obtained toothbrush is used by persons adapted to conventional toothbrushes formed of stiff nylon bristles, but it is ineffective for removing impurities between the periodontal pockets due to end points each with a relatively large diameter.
The toothbrush bristles having the above properties are applied to production of respective toothbrush products. However, the toothbrush having all properties mentioned above has not been produced yet. Further, in the above techniques, it is difficult to manufacture the toothbrush bristle having a desirable tapered length and an end point with a desired diameter, thus increasing defective rates. Attributable to these problems, all conventional toothbrush products suffer from excessive manufacturing cost.